1. Field of the Invention
The present invention generally relates to the field of a disk drive such as a hard disk drive, and more particularly to the improvement of an access control method for continuously accessing data from a plurality of data tracks on a disk medium.
2. Description of the Related Art
In recent years, disk drives such as hard disk drives have been used as storage devices for storing audio data and video data (generally called AV data) in addition to computer data. A host system such as a personal computer or a digital television set accesses AV data stored in a disk drive through an image recording operation or a sound recording operation and then permits a playback system such as through a display or a speaker to reproduce the data.
Unlike computer data, AV data requires continuous processing. Accordingly, an access operation for AV data has the following characteristics: First, in accessing AV data, higher priority is given to maintaining an arbitrary transfer rate in accordance with the amount of data of, e.g., images or sounds than increasing the accuracy of the data. In order to maintain the transfer rate, the host system sets an arbitrary time limit for access to the disk drive. In the disk drive, an access process is completed within the time limit, thereby maintaining the transfer rate.
Upon accessing AV data, AV data is successively recorded to sequential addresses on a disk recording medium (hereinbelow, simply referred to as a disk), or AV data is successively reproduced from the disk. In this case, an access operation where previously recorded AV data is reproduced from a data track while other AV data is being recorded to another data track designated on the disk is often carried out. In the access operation, a particular access with respect to recording or reproducing is not preferentially executed. Both of the accesses for recording and reproducing are alternately executed.
Generally, the disk drive executes the foregoing access operation in response to a request (a command generated) from the host system. However, when only the access operation is performed in accordance with the request from the host system, the performance of data transfer to/from the host system is degraded. The reason is as follows. Specifically, in the disk drive, the access operation for recording or reproducing designated data to/from the disk requires processing time (namely, the time required for preparation processing) for the seek operation of the head, which is not concerned with data transfer.
General disk drives use a method for continuous access to sequential data between the accesses of data requested from the host system. In the access operation during reproduction, after requested data on the disk is accessed, a look-ahead operation to continuously access data from consecutive data sectors following the sector of the requested data is executed. On the other hand, in the access operation during recording, a write operation to continuously write requested data (write data), which is transferred from the host system to a buffer memory in the drive, to consecutive data sectors is executed.
The above method is effectively used to increase the performance of data transfer (in some cases, called host transfer) to/from the host system. However, in the above-mentioned alternate access operation, when the sequential access operations are alternately executed to the data tracks, a situation where the look-ahead operation upon reproduction is hardly executed occurs. Therefore, when the usual continuous access method is used, the performance of the host transfer cannot always be increased in the alternate access operation upon reproducing AV data.
In the general disk drive, when the continuous access method is used and the look-ahead operation is executed in the access operation during reproduction, the performance of the host transfer can be increased. However, as mentioned above, in the access operation to sequentially and alternately access data upon, particularly, reproducing AV data, the look-ahead operation upon reproduction is hardly executed due to influences of the number of seek operations of a head to the data tracks having different access targets and the rotation waiting time of the disk. Accordingly, the performance of the host transfer cannot always be increased. As related art, methods for performing each access in a minimum time in the access operation for sequentially and alternately executing accesses have been proposed (for example, refer to Jpn. Pat. Appln. KOKAI Publication No. 6-12188). However, in the related art, such a situation that the look-ahead operation cannot be executed is not overcome. Therefore, the performance of the host transfer cannot be increased.